1. Field of the Invention
The present invention relates to a novel polycarbonate resin composition. More particularly, the present invention relates to a novel polycarbonate resin composition showing a lesser degree of molecular weight decrease which is accompanied with compounding of inorganic fillers or inorganic pigments to a polycarbonate resin. It also relates to a novel polycarbonate resin composition having excellent moldability and providing molded articles having excellent appearance, mechanical properties, such as impact resistance, bending modulus and the like, and degree of whiteness.
2. Description of the Related Art
Polycarbonate resins have excellent mechanical strength, particularly impact strength, electric properties, transparency and the like and have been widely applied as engineering plastics in various fields, such as electric and electronic instruments, automobiles and the like.
When the polycarbonate resins having the properties described above are used as exterior materials of automobiles and the like, they are generally modified with inorganic fillers or inorganic pigments. The following examples can be mentioned as the polycarbonate resin modified with inorganic fillers or inorganic pigments: a material in which an inorganic filler is added and stiffness is increased while the appearance is kept excellent; a material in which an inorganic filler is added and the coefficient of linear expansion is decreased while the appearance is kept excellent; a material which is colored by addition of an inorganic pigment; a material in which an inorganic filler or an inorganic pigment is added and solvent resistance and impact resistance are improved by further addition of thermoplastic polyester resins or rubbery elastomers; and the like materials.
For the material in which an inorganic filler is added and stiffness is increased while appearance is kept excellent and the material in which an inorganic filler is added and coefficient of linear expansion is decreased while the appearance is kept excellent, talc, mica, potassium titanate whisker or the like is used recently in place of glass fiber which has heretofore been used.
However, when an inorganic filler or an inorganic pigment is compounded with a polycarbonate resin, problems arise that molecular weight of the polycarbonate is decreased significantly, that impact resistance is also decreased significantly to cause deterioration of characteristic properties of polycarbonate resin and that heat stability of the resin in a molding apparatus is diminished by the decrease of molecular weight.
As the inorganic coloring pigment for white colored articles, white pigments, such as zinc sulfide, zinc oxide, titanium oxide and the like, are used. For example, when titanium oxide which is the representative white pigment among them is compounded with a polycarbonate resin, another problem arises that degree of whiteness is decreased in addition to the decrease of heat stability in a molding apparatus by the decrease of molecular weight.
For the purpose of solving the problems, for example, a polycarbonate resin system comprising inorganic pigments (mainly titanium oxide) and an antioxidant [tetrakis(2,4-di-tert-butylphenyl)-biphenylene diphosphonite] was utilized in a technology disclosed in Japanese Patent Application Laid Open No. 1982-151644 with the object of improving the heat stability during molding (improving degree of whiteness and decrease of color change).
However, the effect of improvement of the heat stability of the system containing a white pigment by the disclosed technology is insufficient.
Coloring materials of inorganic pigments have a problem that hydrolysis of a polycarbonate occurs and molecular weight is decreased when the system is made alkaline or acidic, particularly alkaline, by the presence of the pigments, because polycarbonate resins have carbonic acid ester linkages in the molecule.
The material in which an inorganic filler or an inorganic pigment is added and solvent resistance and impact resistance are improved by the addition of thermoplastic polyester resins or rubbery elastomers has a problem that the system is made alkaline or acidic when an active group, such as the active hydroxyl group, is present on the surface of the inorganic filler. This condition causes decomposition of the polycarbonate resin, accelerates deterioration of physical properties and decreases stability of the process.
Extensive studies were undertaken by the present inventors to develop a polycarbonate resin composition which can suppress decrease of molecular weight of the polycarbonate and has excellent solvent resistance, impact resistance and degree of whiteness by solving the problems described above.
As the result of such studies, it was discovered that a polycarbonate resin composition providing molded products having the desired properties can be obtained by compounding an organopolysiloxane having an organoxysilyl group together with an inorganic filler or an inorganic pigment, or, according to desire, a polyester resin and a rubbery elastomer, into a polycarbonate resin. The present invention was completed on the basis of the discovery.